1. Field of the Invention
The present invention relates to an image recorder for fixing an image recording material to the outer peripheral surface of a recording drum and rotating the recording drum while moving a recording head in a subscanning direction parallel to the rotational axis of the recording drum and applying a laser beam thereby recording a two-dimensional image on the image recording material. More particularly, the present invention relates to an image recorder recording an image on an image recording material generating gas by thermal reaction. It is assumed that the term “gas” includes not only pure gas constituents such as sublimates generated from the image recording material but also a gas mixture of solid components such as dust and ash.
2. Description of the Background Art
In an image recorder employing an image recording material generating gas, the gas may adhere to an objective lens of a recording head or the like to tarnish the surface of the objective lens and deteriorate the quality of an image formed on the image recording material. In order to solve this problem, Japanese Patent Application Laying-Open Gazette No. 2000-56400 discloses a technique of diffusing the aforementioned gas by producing an air stream intersecting with a laser beam emitted from a recording head for preventing the gas from adhering to an objective lens of the recording head.
FIG. 8 is an explanatory diagram schematically showing a recording drum 101 and a recording head 108 in a conventional image recorder. A plate 100 employed as an image recording material is fixed to the outer peripheral surface of the recording drum 101 with a front clamp 102 and a rear clamp 103. The recording head 108 applies a laser beam to the plate 100 for recording images. This recording head 108 comprises a gas diffusion/suction unit 180. The gas diffusion/suction unit 180 injects clean air from an air injection port 182 and sucks the atmosphere from a gas suction port 183 thereby forming an air curtain in front of an objective lens 186 for preventing the gas from adhering to the objective lens 186.
The image recorder shown in FIG. 8 diffuses gas etc. generated from the plate 100 with the air injected from the air injection port 182 and sucks the atmosphere containing the diffused gas from the gas suction port 183. Thus, the image recorder can suck most of the gas generated from the plate 100 through the suction port 183.
In recent years, however, a recording material generating a large quantity of gas has been employed due to development of the so-called processless printing plates requiring no development or the like after image recording, and it is apprehended that the image recorder cannot completely suck the entire gas through the aforementioned suction port 183.
In order to improve gas collection efficiency, the area of the gas suction port 183 of the gas diffusion/suction unit 180 may be enlarged. If the gas diffusion/suction unit 180 fixed to the recording head 108 is enlarged in scale, however, the recording head 108 may be hindered from moving in a subscanning direction.